Canning machines are known in the prior art. One type of machine used in commercial canning secures an end to a can body after the product has been placed in the can by formation of a folded double seam. An example of a double seam forming machine which secures top ends to can bodies is shown in U.S. Pat. No. 3,465,703. The disclosure of this patent is incorporated herein by reference. A second example is shown in the published PCT Application No. PCT/US97/14471 which was filed on Aug. 18, 1997. The disclosure of this Application is incorporated herein by reference.
During the process of using a commercial canning device to close a can, a seaming roll must be initially positioned with respect to a cooperating chuck. The relationship of the seaming roll to the chuck must be precise in order to make a proper seam.
One method of positioning the seaming roll is to use a seaming lever which houses a worm gear. This is used in conjunction with a worm pinion which is formed on one end of a shank. The worm pinion end of the shank is connected to a seaming lever and the other end of the shank is connected to a seaming roll lever. The seaming roll lever is attached to the seaming roll, which is used with the chuck to create the seam. The worm gear in the seaming lever engages the worm pinion on the shank. Turning the worm gear in one direction rotates the shank around its axis in one direction, moving the seaming roll either closer to or farther away from the chuck. Rotating the worm gear in the opposite direction will rotate the shank in the opposite direction, thus moving the seaming roll in the opposite direction.
Generally, the seaming roll position determines the final thickness of the can seam. Its precise placement is difficult to achieve using the current design because rotating the worm gear produces relatively large rotations of the shank used to control the position of the seaming roll. A worm gear associated with a 30 tooth worm pinion, typical for this manufacturing use, would create a 12 degree rotation of the associated shank for every 360° rotation of the worm gear. Although this is an impressive reduction, it still provides insufficient control to precisely position the seaming roll.
Further refinement of the worm gear and worm pinion can create marginal, but not sufficient, additional reduction. In part this is because any additional reduction comes at the price of structural integrity. Very fine, closely packed threads and teeth produce large reductions. Unfortunately threads and teeth which produce sufficient reduction for precise placement may not be sturdy enough to withstand the rigors of a manufacturing environment. In addition, creating additional reduction by using a finer worm gear creates a new problem by eliminating the ability to make larger rotations of the shank easily.
Thus, there exists a need for an adjustable seaming lever which has dual adjustment capabilities, a coarse adjustment with reduction which approximates the rotational reduction of a standard worm gear and a fine adjustment which produces far greater rotational reduction. There further exists a need for this adjusting apparatus to be sturdy, in order to withstand the forces to which it is subjected during the canning process.